The disclosure of Japanese Patent Application No. 2002-201569 filed on Jul. 10, 2002, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to apparatus and method for controlling a fuel injection amount of an internal combustion engine.
2. Description of Related Art
In an internal combustion engine of an electronically-controlled fuel injection type, fuel is supplied to each of cylinders of the engine through fuel injection immediately before the intake stroke of the cylinder or during the intake stroke. The cylinder to which the fuel needs to be supplied will be hereinafter referred to as xe2x80x9cparticular cylinderxe2x80x9d or xe2x80x9cfuel injection cylinderxe2x80x9d. During an operation of the engine, an amount of intake air that is drawn into the fuel injection cylinder during the intake stroke is initially calculated, and fuel is injected in an amount corresponding to the calculated intake air amount, by the time when a corresponding intake valve is closed at the end of the intake stroke (i.e., by a point of time when the intake valve shifts from an open state to a closed state) at the latest. Depending upon the case, the fuel is injected before the start of the intake stroke.
To enable the internal combustion engine to operate in the manner as described above, a control apparatus of an internal combustion engine as disclosed in, for example, U.S. Pat. No. 6,014,955 predicts an opening angle of a throttle valve as one of operating state quantities of the engine up to the time of closing of the intake valve of the fuel injection cylinder, and predicts an amount of intake air that will be present in the fuel injection cylinder at the time of closing of the intake valve, based on the predicted throttle opening and an air model that models the behavior of air in the intake system of the engine. The control apparatus then injects fuel into the cylinder in an amount corresponding to the predicted intake air amount.
The conventional control apparatus as described above may suffer from the following problem: if a difference (or estimation error) arises between the predicted intake air amount and the actual intake air amount, for example, due to a difference between the predicted throttle opening and the actual throttle opening, the fuel injection amount calculated by the control apparatus deviates from an appropriate value, and the air/fuel ratio fluctuates or deviates from a target value.
In the meantime, there is widely known a fuel injection amount control apparatus that controls the fuel injection amount in a feedback fashion. More specifically, in order that the air/fuel ratio of an air-fuel mixture introduced into the engine coincides with a target air/fuel ratio, the control apparatus uses an air/fuel ratio sensor provided in an exhaust passage of the engine to detect the air/fuel ratio of exhaust gas, and controls the fuel injection amount in a feedback manner depending upon a deviation of the detected air/fuel ratio from the target air/fuel ratio. This arrangement makes it possible to reduce a steady-state deviation of the air/fuel ratio of the air-fuel mixture from the target air/fuel ratio due to, for example, changes in the properties of fuel, variations in the performance of injectors resulting from manufacturing errors, and the like.
It is, however, to be noted that the air/fuel ratio measured by the air/fuel ratio sensor is the air/fuel ratio of exhaust gas that is emitted from the combustion chamber after combustion of an air-fuel mixture supplied to the engine in the past, and then reaches the air/fuel ratio sensor through the exhaust passage. Therefore, the feedback control involves a large wasteful time. Furthermore, if the feedback control utilizing the detected air/fuel ratio is designed to promptly compensate for fluctuations in the air/fuel ratio due to estimation errors in the predicted intake air amount, the feedback control gain needs to be increased. If the control gain is excessively large, the air/fuel ratio may undergo hunting.
It is therefore an object of the invention to provide fuel injection amount control apparatus and method of an internal combustion engine, which are able to promptly compensate for estimation errors in the intake air amount, while at the same time making use of the advantages of the feedback control, so that the air/fuel ratio of an air-fuel mixture supplied to the engine can be stably made equal to the target air/fuel ratio.
To accomplish the above and/or other object(s), a fuel injection amount control apparatus according to a first aspect of the invention includes a predicted in-cylinder intake air amount calculating unit B1, a basic fuel injection amount calculating unit B3, an actual in-cylinder intake air amount calculating unit B4, a feedfoward correction amount calculating unit (B5-B7), a feedforward fuel injection amount calculating unit A1, an air/fuel ratio sensor 69, a feedback correction amount calculating unit (B8-B11), a final fuel injection amount calculating unit A2 and a fuel injector 39, as shown in FIG. 2. The control apparatus injects a fuel having the calculated final fuel injection amount into a particular cylinder during a particular intake stroke.
The control apparatus including the above-indicated units calculates a predicted in-cylinder intake air amount (klfwd) based on a predicted operating state quantity of the engine, and calculates a basic fuel injection amount (finjb(k)) based on the predicted in-cylinder intake air amount. On the other hand, the control apparatus calculates an actual in-cylinder intake air amount (klcyl(kxe2x88x921)) from the actual (confirmed) engine operating state quantity, and calculates a feedforward fuel injection amount (finjfwd(k)) by correcting an excess or shortage of fuel due to a difference between the predicted in-cylinder intake air amount and the actual in-cylinder intake air amount by using a feedforward correction amount (finjk(k)). Also, the control apparatus calculates a feedback correction amount (finjfb(k)) for reducing a deviation between the actual air/fuel ratio (abyfs) detected by the air/fuel ratio sensor and an air/fuel ratio of an air-fuel mixture that is determined by the feedforward fuel injection amount (finjfwd(k)), and obtains a final fuel injection amount (finjfinal(k)) by correcting the feedforward fuel injection amount by using the feedback correction amount. In the following, each of the above-indicated units will be described.
The predicted in-cylinder intake air amount calculating unit B1 predicts an operating state quantity of the engine to be established at a point of time ahead of the current point of time. For example, the engine operating state quantity is an opening angle of a throttle valve of the engine, or the like, which is required for predicting or estimating the intake air amount of the engine. The predicted in-cylinder intake air amount calculating unit then calculates the predicted in-cylinder intake air amount (klfwd) that is an amount of intake air drawn into the particular cylinder of the engine during the particular intake stroke, based on the predicted engine operating state quantity, at a point of time before completion of the particular intake stroke of the particular cylinder. Namely, this unit predicts, prior to completion of a certain intake stroke, an amount of intake air drawn in this intake stroke, based on a future engine operating state quantity.
The basic fuel injection amount calculating unit B3 calculates the basic fuel injection amount (finjb(k)) for achieving a target air/fuel ratio, based on the predicted in-cylinder intake air amount thus calculated and the target air/fuel ratio. For example, the basic fuel injection amount (finjb(k)) is calculated by dividing the predicted in-cylinder intake air amount (klfwd) by the target air/fuel ratio (abyfref).
The actual in-cylinder intake air amount calculating unit B4 calculates the actual in-cylinder intake air amount (klcyl(kxe2x88x921)), which is an amount of intake air drawn into the particular cylinder during an intake stroke one cycle before the particular intake stroke of the particular cylinder. More specifically, at a point of time after the engine operating state quantity used by the predicted in-cylinder intake air amount calculating unit for calculating the predicted in-cylinder intake air amount with respect to the intake stroke one cycle before the particular intake stroke is confirmed, the actual in-cylinder intake air amount calculating unit calculates the amount of intake air drawn into the particular cylinder during the intake stroke one cycle before the particular intake stroke, as the actual in-cylinder intake air amount (klcyl(kxe2x88x921)), based on the actual engine operating state quantity thus confirmed. Thus, the actual in-cylinder intake air amount (klcyl(kxe2x88x921)) is calculated based on the confirmed engine operating state quantity (that includes no prediction/estimation error), thereby providing an accurate in-cylinder intake air amount.
The feedforward correction amount calculating unit (B5-B7) calculates the feedforward correction amount (finjk(k)) based on the predicted in-cylinder intake air amount for the intake stroke one cycle before the particular intake stroke and the actual in-cylinder intake air amount for the intake stroke one cycle before the particular intake stroke. The feedforward correction amount is determined so as to compensate for an excess or a shortage of the basic fuel injection amount for the intake stroke one cycle before the particular intake stroke, which excess or shortage is caused by a difference between the predicted in-cylinder intake air amount for the intake stroke one cycle before the particular intake stroke of the particular cylinder and the actual in-cylinder intake air amount for the intake stroke one cycle before the particular intake stroke.
The feedforward fuel injection amount calculating unit A1 calculates the feedforward fuel injection amount (finjfwd(k)) by correcting the basic fuel injection amount (finjb(k)) for the particular intake stroke of the particular cylinder by using the feedforward correction amount (finjk(k)).
The air/fuel ratio sensor 69 detects the air/fuel ratio (abyfs) of exhaust gas emitted from the engine. The feedback correction amount calculating unit (B8-B11) calculates the feedback correction amount (finjfb(k)) for reducing a deviation between the air/fuel ratio (abyfs) detected by the air/fuel ratio sensor and an air/fuel ratio (klcyl(kxe2x88x92N)/fc(kxe2x88x92N)) of an air-fuel mixture corresponding to the exhaust gas whose air/fuel ratio is detected by the air/fuel ratio sensor. The air/fuel ratio of the air-fuel mixture is determined based on the feedforward fuel injection amount (finjfwd) calculated by the feedforward fuel injection amount calculating unit with respect to a past intake stroke of the particular cylinder during which the air-fuel mixture was introduced into the cylinder. The feedback correction amount calculating unit calculates the feedback correction amount based on the air/fuel ratio of the above-described air-fuel mixture and the detected air/fuel ratio.
The final fuel injection amount calculating unit A2 calculates the final fuel injection amount (finjfinal(k)) by correcting the feedforward fuel injection amount (finjfwd(k)) calculated with respect to the particular intake stroke of the particular cylinder, by using the feedback correction amount (finjfb(k)). The fuel injector 39 injects a fuel having the final fuel injection amount into the particular cylinder during the particular intake stroke.
In the above manner, an excess or shortage of the basic fuel injection amount due to a prediction/estimation error in the intake air amount for the intake stroke one cycle before the particular intake stroke is promptly compensated for by the feedforward correction amount that reflects the prediction/estimation error, so that the corrected fuel injection amount can be used for the coming and subsequent intake strokes In other words, the feedforward system that calculates the feedforward fuel injection amount compensates for a deviation of the fuel injection amount that depends on prediction/estimation of the in-cylinder intake air amount, from an appropriate value thereof, without relying upon the air/fuel ratio detected by the air/fuel ratio sensor.
Also, the feedback correction amount is used for surely compensating for a steady-state deviation of the air/fuel ratio from the target air/fuel ratio due to, for example, changes in the properties of fuel and variations in the performance of the injectors. In other words, the feedback system that provides the feedback correction amount compensates for a steady-state excess or shortage of the feedforward fuel injection amount, by using the detected air/fuel ratio. Thus, when the engine is in a transient operating state, in particular, the feedback control performed based on the detected air/fuel ratio does not need to compensate for transient fluctuations in the air/fuel ratio due to prediction/estimation errors in the in-cylinder intake air amount. Therefore, the gain of the feedback control can be set small, resulting in stable air/fuel ratio control. Furthermore, the feedforward system and the feedback system of the fuel injection amount control apparatus are adapted to compensate for excesses or shortages of the fuel injection amount due to different factors, and therefore the controls of these systems do not interfere with each other, and are free from instability due to otherwise possible interference.
According to a second aspect of the invention, there is provided a fuel injection amount control apparatus which includes a predicted in-cylinder intake air amount calculating unit B1, a basic fuel injection amount calculating unit B3, a feedforward fuel injection amount calculating unit A1, a feedforward in-cylinder fuel amount calculating unit B6, an actual in-cylinder intake air amount calculating unit B4, a feedforward target in-cylinder fuel amount calculating unit B5, a feedforward correction amount calculating unit B7, an air/fuel ratio sensor 69, a sensor detected in-cylinder fuel amount calculating unit B8, a feedback correction amount calculating unit B11, a final fuel injection amount calculating unit A2, and a fuel injector 39. The control apparatus thus constructed injects a fuel having the calculated final fuel injection amount into a particular cylinder for a particular intake stroke.
The control apparatus including the above-indicated units calculates a predicted in-cylinder intake air amount (klfwd) based on a predicted operating state quantity of the engine, calculates a basic fuel injection amount (finjb(k)) based on the predicted in-cylinder intake air amount, and calculates a feedforward fuel injection amount (finjfwd(k)) by correcting the basic fuel injection amount by using a feedforward correction amount (finjk(k)). The control apparatus also calculates, as a calculated in-cylinder fuel amount fc(kxe2x88x921), an amount of fuel that is supposed to be introduced into the particular cylinder on the assumption that fuel having the feedforward fuel injection amount was injected for an intake stroke one cycle before the particular intake stroke. The control apparatus further calculates an actual in-cylinder intake air amount (klcyl(kxe2x88x921)) for the intake stroke one cycle before the particular stroke, from the actual (confirmed) engine state operating quantity, and calculates a feedforward target in-cylinder fuel amount (fcref(kxe2x88x921)), which is an amount of fuel that should have been actually supplied to the particular cylinder, by, for example, dividing the actual in-cylinder intake air amount by the target air/fuel ratio (abyfref). Then, the control apparatus calculates the feedforward correction amount (finjk(k)) based on the calculated in-cylinder fuel amount and the feedforward target in-cylinder fuel amount.
On the other hand, the control apparatus detects the air/fuel ratio of the exhaust gas, and calculates a sensor detected in-cylinder fuel amount (fcsns(kxe2x88x92N)), based on the actual in-cylinder intake air amount (klcyl(kxe2x88x92N)) obtained when an air-fuel mixture that gives rise to the detected air/fuel ratio was introduced into the cylinder (namely, the actual in-cylinder intake air amount for an intake stroke a predetermined cycles before the particular intake stroke), and the detected air/fuel ratio (abyfs). The control apparatus then calculates a feedback correction amount (finjfb(k)) for reducing a deviation between the calculated in-cylinder fuel amount (fc(kxe2x88x92N)) calculated with respect to the intake stroke the predetermined number of cycles before the particular intake stroke, and the sensor detected in-cylinder fuel amount (fcsns(kxe2x88x92N)). The control apparatus then obtains a final fuel injection amount finjfinal(k) by correcting the feedforward fuel injection amount by using the feedback correction amount.
In the control apparatus as described above, too, an excess or shortage of the basic fuel injection amount due to a prediction/estimation error in the intake air amount for the intake stroke one cycle before the particular intake stroke is promptly compensated for by the feedforward correction amount that reflects the prediction/estimation error, so that the corrected fuel injection amount can be used for the coming and subsequent intake strokes. In other words, the feedforward system that calculates the feedforward fuel injection amount compensates for a deviation of the fuel injection amount that depends upon prediction/estimation of the in-cylinder intake air amount, from an appropriate value thereof, without relying upon the air/fuel ratio detected by the air/fuel ratio sensor.
Also, the feedback correction amount is determined based on a difference between the sensor detected in-cylinder fuel amount as an amount of fuel actually supplied to the particular cylinder for the intake stroke the predetermined number of cycles before the particular intake stroke, and the calculated in-cylinder fuel amount that should have been actually supplied for the intake stroke the predetermined number of cycles before the particular intake stroke. The thus determined feedback correction amount is used for surely compensating for a steady-state deviation of the air/fuel ratio from the target air/fuel ratio due to, for example, changes in the properties of fuel and variations in the performance of the injectors. In other words, the feedback system that provides the feedback correction amount compensates for a steady-state excess or shortage of the feedforward fuel injection amount, by using the detected air/fuel ratio.
Accordingly, when the engine is in a transient operating state, in particular, the feedback control performed based on the detected air/fuel ratio does not need to compensate for transient fluctuations in the air/fuel ratio due to prediction/estimation errors in the in-cylinder intake air amount. Therefore, the gain of the feedback control can be set small, resulting in stable air/fuel ratio control. Furthermore, the feedforward system and the feedback system of the fuel injection amount control apparatus are adapted to compensate for excesses or shortages of the fuel injection amount due to different factors, and therefore the controls of these systems do not interfere with each other, and are free from instability due to otherwise possible interference.
According to a third aspect of the invention, there is provided a fuel injection amount control apparatus which includes a predicted in-cylinder intake air amount calculating unit B1, a basic fuel injection amount calculating unit B3, a feedforward fuel injection amount calculating unit A1, a feedforward in-cylinder fuel amount calculating unit B6, an actual in-cylinder intake air amount calculating unit B4, a feedforward target in-cylinder fuel amount calculating unit B5, a feedforward correction amount calculating unit B7, an air/fuel ratio sensor 69, a feedback correction amount calculating unit B11, a final fuel injection amount calculating unit A2 and a fuel injector 39. The control apparatus thus constructed injects fuel having the calculated final fuel injection amount into a particular cylinder for a particular intake stroke.
The control apparatus calculates various amounts, except a feedback correction amount, in similar manners to the fuel injection amount control apparatus according to the first or second aspect of the invention. Thus, the feedback correction amount calculating unit of the control apparatus will be described. The feedback correction amount calculating unit calculates a feedback correction amount finjfb(k) for reducing a deviation between a calculated air/fuel ratio (=klcyl(kxe2x88x92N)/fc(kxe2x88x92N)) and the air/fuel ratio (abyfs) detected by the air/fuel ratio sensor, based on the calculated air/fuel ratio and the detected air/fuel ratio. The calculated air/fuel ratio is determined based on the actual in-cylinder intake air amount (klcyl(kxe2x88x92N)) obtained when an air-fuel mixture that gives rise to the air/fuel ratio detected by the air/fuel ratio sensor 69 was introduced into the cylinder (namely, the actual in-cylinder intake air amount for an intake stroke a predetermined number of cycles before the particular intake stroke of the particular cylinder), and a calculated in-cylinder fuel amount fc(kxe2x88x92N) calculated by the feedforward in-cylinder fuel amount calculating unit with respect to the intake stroke the predetermined number of cycles before the particular intake stroke. The feedback correction amount calculating unit calculates the feedback correction amount so that the air/fuel ratio calculated by the feedforward system and the detected air/fuel ratio become equal to each other.
In the fuel injection amount control apparatus according to the third aspect of the invention, too, an excess or shortage of the basic fuel injection amount due to a prediction/estimation error in the intake air amount for the intake stroke one cycle before the particular intake stroke is promptly compensated for by the feedforward correction amount, so that the corrected fuel injection amount can be used for the coming and subsequent intake strokes. Also, the feedback correction amount is used for compensating for a steady-state deviation of the air/fuel ratio from the target air/fuel ratio due to, for example, changes in the properties of fuel and variations in the performance of the injectors.
Accordingly, when the engine is in a transient operating state, in particular, the feedback control performed based on the detected air/fuel ratio does not need to compensate for transient fluctuations in the air/fuel ratio due to prediction/estimation errors in the in-cylinder intake air amount. Therefore, the gain of the feedback control can be set small, resulting in stable air/fuel ratio control. Furthermore, the feedforward system and the feedback system of the fuel injection amount control apparatus are adapted to compensate for excesses or shortages of the fuel injection amount due to different factors, and therefore the controls of these systems do not interfere with each other, and are free from instability due to otherwise possible interference.
In the fuel injection amount control apparatuses as described above, the feedforward in-cylinder fuel amount calculating unit is preferably arranged to calculate the calculated in-cylinder fuel amount by using a forward model of a fuel behavior model representing the behavior of fuel deposited on a member that forms an intake passage of the engine. Also, the basic fuel injection amount calculating unit is preferably arranged to calculate the basic fuel injection amount by using an inverse model of a fuel behavior model representing the behavior of fuel deposited on a member that forms the intake passage of the engine.
With the above arrangements, the amount of fuel deposited on a member or members that form or define the intake passage is taken into consideration, and therefore the final fuel injection amount is calculated with further improved accuracy, thus making it possible to make the air/fuel ratio of the engine closer to or substantially equal to the target air/fuel ratio.